This invention relates to a hydraulic drive liquid transfer pump system for transferring liquid from a delivery vehicle.
Offloading liquid from a delivery vehicle has been accomplished in a number of ways. One arrangement involves the use of an onboard electric motor to drive a liquid pump. The motor is generally driven by power derived from an electric generator associated with the delivery vehicle. This system has encountered several disadvantages. One disadvantage is that the capacity of electric generator and associated electric motors is such that the units have relatively low power ranges resulting in relatively long offloading times. Larger units with increased power capability are too bulky and heavy to be mounted on the delivery vehicle. In addition, because electrical systems operated in high load service are not generally high reliability systems, there has been experienced considerable downtime and maintenance expense.
Another arrangement employed to offload liquid from a delivery vehicle has been to employ an internal combustion engine to drive the liquid pump. However, because many of the liquids to be offloaded, such as petroleum products or liquid oxygen, pose a safety hazard if near an internal combustion engine, the engine and the liquid pump must be separated by a substantial distance. The internal combustion engine is connected to the liquid pump by mechanical means. This arrangement, involving relatively long mechanical coupling arrangements, has the disadvantage of requiring excessive maintenance and has encountered other operating problems.
In response to these problems, there have been employed system involving tractor-trailer arrangements with an internal combustion engine mounted on the trailer and connected to the liquid pump by a hydraulic system, generally including a hydraulic pump connected to the internal combustion engine and hydraulic lines forming a circuit with the hydraulic pump and a hydraulic motor. The hydraulic motor drives the liquid pump. One such system is described in U.S. Pat. No. 4,177,017 to Schultz.
One disadvantage of the above-described hydraulic system is the relatively low capacity and consequent relatively long liquid pumping times associated with the system. This is primarily due to the limited capacity of the trailer-mounted internal combustion engine. One way to increase the amount of power available to the liquid transfer system is to utilize the reactor motor instead of the trailer-mounted motor. However, the use of the tractor motor, which involves connections from the tractor to the trailer, and the associated higher capacities and/or flow rates resulting from the increased power, give rise to a number of significant safety-related problems. These problems are particularly acute when the liquid to be offloaded is a cryogenic liquid such as liquid oxygen, nitrogen or argon.
One problem is that since the liquid delivery unit is to be separated into tractor and trailer portions, it is imperative that the unit not move or be moved in any fashion during the offloading operation. This was not a problem previously because the trailer portion could be disengaged from the tractor portion and in addition there were no hydraulic connections which could be severed between tractor and trailer.
Another problem which arises with increased capacity is increased hydraulic fluid temperature resulting from greatly increased friction and other energy losses. This heat energy may be removed by a cooler which can be employed to ensure that the hydraulic fluid temperature levels are kept at acceptably low values. However, should there be any malfunction within the cooling circuit, the fluid temperature would increase rapidly to a level which would cause failure of some of the system components. Such a condition would be very unsafe especially if the unit were handling a cryogenic fluid such as liquid oxygen.
Another safety problem associated with running at increased capacity is related to the fluid reservoir level or fluid content within the hydraulic circuit. If the fluid inventory is low, the hydraulic pumping unit would not be able to transmit the increased power capacity associated with the system and can overheat or fail in some other mechanical mode.
Still another safety problem associated with running at increased capacity is related to the particulate content of the hydraulic fluid. It is important for the hydraulic fluid to be clean with low particulate content because, since the hydraulic pumping unit has high capacity and low clearance components, any significant particulate content in the hydraulic fluid would readily score or otherwise harm the mechanical clearances and cause malfunction or mechanical degradation of the system.
It is desirable to decrease the time required to offload liquid from a delivery vehicle. One means of accomplishing this is to utilize the tractor motor of a tractor-trailer delivery vehicle to supply power to the delivery system. This would result in a delivery system of increased capacity. Therefore, a liquid transfer pump system which can utilize the tractor motor and also avoid the above-described safety and reliability related problems which arise when such increased capacity is used would be highly desirable.
Accordingly, it is an object of this invention to provide a hydraulic drive liquid transfer pump system which utilizes the tractor motor of a tractor-trailer delivery vehicle to power the delivery system.
It is another object of this invention to provide a hydraulic drive liquid transfer pump system which operates at increased capacity over those heretofore available.
It is another object of this invention to provide a hydraulic drive liquid transfer pump system which can operate at increased capacity while avoiding the abovedescribed safety and reliability problems.